The reduction of CO2 emission is one of the greatest concerns in combating the catastrophic “global warming” trend. As a result, the world puts much emphasis on the exploitation of “clean energy” with less or non-emission for both industrial and domestic uses. Natural gas (hereafter abbreviated as “NG”), as compared with coal and petroleum, is considered the most economic “clean” fuel that is used on a large, industrial scale at present and in the near future. In addition, the discovery of huge amount of ocean-bed gas-hydrates increases the recoverable resources of NG substantially. It is expected that, in the long run, the global NG consumption may eventually exceeds all other fossil fuels.
NG is a mixture of hydrocarbon gases, consisting of mainly methane (C1) and a smaller fraction of heavier gaseous hydrocarbons (i.e., ethane, C2; propane, C3; butane, C4; pentane and higher, C5+; sometimes C3+ is called “light oil” as a whole. However, the economic values of these higher hydrocarbon components, when separated and sold as chemical feedstock, are usually much higher than burnt as a fuel. A number of NG processing plants, therefore, have been constructed to extract these valuable materials.
The state-of-the-art NG processing plants generally work on a cryogenic process for efficiently separating the higher hydrocarbon gases In this process, a huge volume of NG is cooled down by expansion to a very low cryogenic temperature around −150° F. Such a process is extremely energy-consuming, and the facility usually comprises many pieces of expensive equipment, notably the molecular-sieve dehydrator, the multiple-flow finned-plate heat exchanger, and the turbo expander-compressor. High capital and operational costs are thus resulted. As a consequence, only a limited fraction of the NG could be processed before consumed as a fuel. Most of the valuable higher hydrocarbon contents was improperly used.
In the past two decades, a number of US patents have been granted in this field, for example, the 13 US patents entitled “hydrocarbon Processing” presented by late Roy E. Campbell, et al., i.e., U.S. Pat. Nos. 4,140,504; 4,157,904; 4,171,964; 4,278,457; 4,854,955; 4,869,740; 4,889,545; 5,555,784; 5,568,737; 5,771,712; 5,881,569; 5,983,664; and 6,182,469. However, most of these patents only proposed some specific improvements to the same cryogenic process. No substantial break-through in NG processing technology has ever been proposed. A more efficient and cost-effective technology for NG procession, therefore, is desirable.
The recent developments in NG refrigeration dehydration technology, e.g., those presented in U.S. Pat. No. 5,664,426, “Regenerative Gas Dehydrator,” 1997, and U.S. Pat. No. 6,158,242, “Gas Dehydration Method and Apparatus,” 2000, provided the basis of a break-through in the NG processing technology. These patents make possible to perform refrigeration dehydration and refrigeration absorption in a single unit.
Accordingly, it is an objective of the present invention to provide a comprehensive NG process and a processor, based on the refrigeration dehydration and absorption technologies, for efficient and cost-effective comprehensive processing of NG. The said processor could simultaneously perform the removal of moisture and the recovery of the higher hydrocarbons (C2+) in a single piece of equipment, thus substantially reducing the capital and operational costs of the NG processing plant.
Another objective of the present invention is to provide an energy-saving comprehensive NG process and a processor that, when processing high pressure NG, does not need external energy for refrigeration.
A further objective of the present invention is to provide a high-efficiency free-piston expander-compressor to provide the required refrigeration.